Conventionally, HE-AAC (high efficiency MPEG (moving picture experts group) 4 AAC (advanced audio coding)) (ISO/IEC14496-3) is known as an encoding method of an audio signal.
In this encoding method, characteristic information is extracted from a high-frequency signal component to be encoded together with a low-frequency signal component (refer to Patent Document 1, for example). At the time of decoding, the low-frequency signal component is mapped to a high-frequency range and a frequency envelope is adjusted based on the information of the high-frequency range included in a code string. In such encoding method, only the characteristic information of the high-frequency signal component is encoded as information regarding the high-frequency signal component, so that it is possible to improve coding efficiency while inhibiting deterioration in audio quality.
In general, in the encoding device which adopts an encoding system to encode only the characteristic information of the high-frequency range as the information regarding the high-frequency component, there often is a case in which a code amount of the high-frequency range is extremely smaller than that of a low-frequency range and adjusting flexibility of the code amount of the high-frequency range is small. Therefore, a method is such that the information regarding the high-frequency signal component is first encoded and then the low-frequency signal component is encoded with a remaining code amount. Such a configuration may avoid a complicated configuration of the encoding device and prevent a large calculation amount.